Directional output magnetron system



March 15, 1960 D. A. WILBUR DIRECTIONAL OUTPUT MAGNETRON SYSTEM Filed June 13, 1958 /n venfor: Dona/0' A. WIYbur,

' His Attorney.

7 2,928,986 V H DIRECTIONAL OUTPUT MAGNETRON SYSTEM Donald A. Wilbur, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Application June 13, B58, Serial N5. 741,851 2 Claims. (Cl. 315-39 The present invention relates to an improved magnetron system and particularly to an improved output circuit which is directionally coupled to the anode line of the magnetron throughout a substantial length of that line.

Magnetron oscillator systems are frequently operated in such a manner that a standing electromagnetic wave is produced on the anode delay line and the output energy coupled from a local region of the anode delay line. In such a system, the impedance presented to the electron beam by the anode line is highly dependent upon the output load. and upon changes in the value of the load and upon the reflections resulting from the presence of the output coupling. These conditions cause changes in the power input and efliciency of the system as well as back heating of the cathode with changes in load. In accordance with an important aspect of the presen. invention the system is operated with a traveling wave on the anode line from which energy is coupled directionally through an output wave guide or transmission line to a desired load at one end of the wave guide or transmission line. Any reflected energy'is dissipated in a dummy load terminating the other end of the output guide or line and the effect of these reflections on the anode circuit and the above-mentioned effects on output, efiiciency and'hack heating of the cathode minimized. The coupling between the anode line and the output wave guide or transmission line is effective throughout a substantial length of the anode line or at a number of points spaced along the length of the'line. A ratio of 200 to 1 between the measured output powers at the useful load and the dissipative load have been measured and a ratio of 50 to 1 between these outputs is readily obtained in a system tuned over a range of about of a center frequency of 4000 megacycles.

It is an important object' of the present invention to provide an improved directional output system for a time netron' oscillator.

, It is another object of my invention to provide an improved directional output system for a magnetron which minimiies the detrimental eifects of the load circuit parameters on the operation of the magnetron.

Further objects and advantages of my invention will become apparent as the following description proceeds, reference being had to the accompanying drawing in w i 7 Figure'l is" a plan view partially broken away of a magnetron oscillator system embodying my invention;

Figure 2 is an elevational view in section taken along nae 2- 2 of Figuie' 1;

Figure 3 is an enlarged elevational View in section of a'por'tion of the system shown in Figure 2;

, Figure 4 is an enlarged view in section taken along the liiie" 4 4' of Figure 3'; V

Figure 5 is' a plan view of a modified invention, and

Figure 6 is an elevational view taken along the line 6-6 of Figure 5. p

Referring now to the drawing, I have shown my inventien embodied in a magnetron system includinga genera'lly annular wave guide 10 centrally apertured to receive a magnetron type of discharge device l 'l liatiing the anode terminalslZ and 13 therec'f coupled to the form of my amass Patented Mar. 15, 1960 2. circular end walls 14' and 15 of the annular guide. A generally spiral coupling conductor 16 substantially sufrcu'nds the discharge device 11 in the region between the anode terminals Hand 13 and has the opposite erids thereof connected respectively with the'cen'ter conductors 1:7 and 18 ofou't'put concentric transmission lines 191' As illustrated the central conductors extend through the upper and lower" end walls 14 and 15 of the wave guide respectively and are insulated therefrom by suitable insulating sleeves 2t} and 21 which are sealed to the guide and the conductors 17 and 18. In the particular embodiment' illustrated the outer conductors 22 of the concentric lines are formed of metallic braid which is brazed or otherwise secured to the outer surfaces of the end walls 14 and 15. Before describing further the output coupling system of the present invention the physical structure of the magnetron device of the illustrated embodiment of my invention will be briefly described.

The envelope of the device is made up of a stack of alternately arranged metal and ceramic members, the metal members forming the terminals of the device and the ceramic members forming the insulating spacers therefor. As shown in the drawing, the annular anode terminals 12 and 13 are separated by a ceramic cylinder 23 and an annular grid terminal 24 is separated from the anode terminal 13 by a ceramic cylinder 25. The envelope iscompleted by a pair of disk-like cathode terminals 26 and27 which form the ends of the eiiyelop'e and are separated from the anode terminal 12 and the gridterininal 24, respectively, by ceramic cylinders 28 and 29. v

The magnetron device illustrated is of the interdigital type and the anode assembly includes two sets of a'iiially extending anode segments alternately arranged in a cylindrical array and supported concentrically within the envelope by anode terminals 12 and 13, respectively. Alternate segments 36 and 31 are supported respectively, from the anode terminals 12 and 13' so that the two groups of anode segments alternately arranged in the array are connected to a different one of the terminals 12 and l3. The segments are slightly separated to provide aiiially extending interaction gaps.- I

In the specific embodimentiliustr'ated the electrons cf the space charge which interacts with the anode segments are emitted from an area longitudinally displaced from the array of anode segments and the entrance of the'electrons into the region of the interaction gaps is under the control of a generally frusto-conical control electrode 32 supported from the terminal 24 and surrounding: the electron emitting cathode which is, in the particular embodiment illustrated, in the form of a tungsten spiral 33. The cathode 33 is supported atits lower end in a recess formed in an integrally formed boss 34 on the'end cap 27 and the other end is supported from a reduced end portion 35 of a centrally located cylindrical non-emitting post 36 supportedfrom the opposite end cap 26.

As will be well understood by those skilled in the art the device just described is operated by producing a maying cloud of electrons in the space between theanode segments 31) and '31 and the non-emitting cathode post 36. Electrons are liberated by passing a predetermined heater current through the cathode 33 and the number entering the interaction space controlled by suitably adinning the voltage of the control electrode 3 3: suitau ann magnetic field in the interaction space is proylde (not shown) and to a radial electric field provided by a direct current voltage impressed between the noneini'tting post 36 and the anode structure. Under these conditions a rotating and bunched space charge in the interaction space interacts with the high frequency fields across the gaps between adjacent anode sections to eifct d, either by a permanent magnet or an electromagnet electrical length applies both to the coupling loop of the H circuit line and also to the anode interaction structure. This latter electrical length of course depends upon the mode of oscillation of the magnetron which is determined by the correlation of the electric and magnetic fields involved and is exhibited in the operation of the device by the fraction of an electrical wave length from vane to vane or anode segment to anode segment around the anode structure. In the particular embodiment illustrated in Figure 4 there are twelve anode segments and if the tube is operating in the mode which is one electrical wave length around the entire anode circuit, there is a 30 electrical length from anode section to anode section and the electrical and mechanical length around the anode in terms of degrees are equal. This means that a coupling loop may be coupled uniformly to the anode structure over a length of 90 electrical degrees for this mode by coupling over 90 mechanical degrees. In the embodiment illustrated the coupling is made over essentially 360 electrical and mechanical degrees. The coupling may be made to couple to either forward or backward wave oscillations of the magnetron device directionally and the useful output is supplied in one direction to one of the cables H. The transmission line at the other end is terminated in its characteristic impedance 'by a suitable resistor (not shown) connected between the central and outside conductors of the concentric transmission line to provide a substantially reflectionless termination of the line.

In the embodiments of the invention described above the transmission line is coupled to the magnetron uniformly over a substantial electrical length with the length of the transmission line coupling corresponding electrically to the electrical length of the anode circuit over which the coupling is made.

In Figures 5 and 6 I have shown my invention embodied in a magnetron and output system in which the coupling takes place at two or more discrete points distributed along the anode in such a manner that the electrical length of the transmission line between the coupling points corresponds to the electrical length between the two points on the anode line oryto 360 degrees plus the length between the coupling points on the transmission line, that is, if the difierence between the coupling points on the output coupling circuit is 90 electrical degrees, for example, then the distance between the anode sections Where the coupling takes place may be 90 degrees or 360 plus 90 degrees.

Referring now to Figure 5, there is shown simply the anode delay line of a magnetron device having eight vanes 37 extending radially inwardly from a supporting annular ring 38. The envelope and cathode structure have been omitted in the interests of simplification. A directional output coupling circuit is provided by a concentric transmission line wrapped around a substantial portion of the circumference of the anode supporting ring 38. The transmission line includes a central conductor 39 and a cylindrical enclosing conductor 4%. Ring 38 is apertured at 41 and 42 to provide for the entrance of coupling loops 43 and 44 into the region between adjacent anode vanes. One end of the central conductor is terminated in a resistor 45 connected between the end of the central conductor and a closed end of the outer conductor 46 and having a magnitude equal to the characteristic impedance of the line while the other end of the transmission line provides the useful output of the system. The magnetron device illustrated is an eight vane device and, if it is operated in a mode in which the high frequency voltage distribution around the anode line undergoes two complete cycles, it will be apparent that the coupling points are spaced apart 360 plus 90 electrical degrees. This geometry is effective if the electrical length of the concentric transmission line between the two coupling points has the same length or, which is even more practical from a structural point of view, has an electrical length of 90 electrical degrees.

In the foregoing specification two embodiments of my invention have been described. One in which the coupling is uniform and continuous about a substantial portion of the circumference of the magnetron line and the other of which the coupling is made at two or more discrete points. While both couplings illustrated are of the concentric line type it will be apparent that, in its broader aspect, the invention may be applied to other trans-mission line or wave guide systems and the coupling for example may be made by openings into a wave guide surrounding the anode structure. Also, it is apparent to those skilled in the art that the invention is not limited to magnetron devices in which the electrons are axially injected into the interaction space or to any particular type of anode structure. Both the interdigital and vane types having been illustrated by way of example.

While I have shown and described particular embodiments of my invention it will be apparent to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects and I aim, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A directional output magnetron system comprising a magnetron including a cylindrical array of anode segments including two sets alternately arranged, means providing space charge within said array and subjecting the space charge to an axial magnetic field and a radial electric field, a hollow annular wave guide surrounding said array of anode segments and having opposed walls each connected to a different one of said sets, a single turn spiral-shaped coupling conductor surrounding said array of anode segments and positioned within said annular wave guide, concentric transmission line means including center conductors coupled respectively to opposite ends of said coupling conductor and an energy I absorbing termination for the concentric transmission line coupled to one end of said terminating conductor.

2. A directional output magnetron system comprising a magnetron including a cylindrical array of anode segments including two sets alternately arranged, means providing space charge within said array and subjecting the space charge to an axial magnetic field and a radial electric field, a hollow annular wave guide surrounding said array of anode segments and having opposed walls each connected to a different one of said sets, a spiral-shaped coupling conductor positioned within said annular wave guide and surrounding said array of anode segments over an angular extent corresponding to at least one fourth wave length of the traveling wave on said array of anode segments to provide a. directional output circuit, concentric transmission line means including center conductors coupled respectively to opposite ends of said coupling conductor and an energy absorbing termination for the concentric transmission line coupled to one end of said terminating conductor.

References Cited in the file of this patent 

